A method of controlling the thermochemical treatment of workpieces in glow discharge in a medium of treating gases, which involves two operating stages, is already known; the first stage includes workpiece warm-up with simultaneous intensive cathode sputtering on their surface, and during the second one diffusion saturation of workpieces is carried out. In both operating stages the temperature of the workpieces in the working chamber, the temperature variation rate and the frequency of the occurring arc discharges are measured. The measured values of these parameters are compared with the corresponding preset values, and error signals are obtained. These error signals are used to create control signals for the mean value and the amplitude of glow discharge voltage. The control signal for the amplitude of glow discharge voltage regulates the frequency of arc discharges in the working chamber so that it will corespond to its preset value, and the control signal for the mean value of glow discharge voltage regulates the temperature of the treated workpieces so that it will correspond to its preset value.
One disadvantage of the method of controlling the thermochemical treatment in glow discharge in a medium of treating gases is the small efficiency of cathode sputtering during warm-up stage, which is due to the fact that it is impossible to preset such an amplitude of glow discharge voltage which would correspond to a preset intensity of the cathode sputtering. Another disadvantage of this method is the complicated control algorithm requiring simultaneous control of both means value and amplitude of glow discharge voltage. A major disadvantage of the method is the impossibility to obtain a satisfactory reproducibility of the results of workpiece treatment because only the workpiece temperature and the frequency of occurring arc discharges are stabilized, while other characteristic parameters influencing the qualtiy of the workpiece treatment are not intended to be used by this method.
A device for controlling thermochemical treatment of workpieces in glow discharge in a medium of treating gas, which includes a power supply having one output and two control inputs, is known; said first input controlling the mean value of output voltage, and said second input controlling the amplitude of output voltage. It also includes a sensor for workpiece temperature measurement which is connected thermally to the treated workpieces, and its output is joined up by series-connected measuring element for the temperature variation rate, comparing element for the temperature rate, and thermoregulator to the first input of a control unit. The temperature sensor output is also joined up by series-connected second comparing element and second thermoregulator to the second input of the control unit. The output of the second comparing element is applied to the third input of the control unit. The input of a converter for the glow discharge voltage is connected with the output of the power supply. The converter output is applied to the fourth input of the control unit, and through series-connected frequency-to-voltage converter, third comparing element and third thermoregulator to the fifth input of the control unit. In the circuit of power supply and working chamber a current sensor is connected in series; its output being applied to the second input of a sensor for arc discharge frequency. Preset value sources for the workpiece temperature, its variation rate and the frequency of occurring arc discharges are connected with second inputs of the corresponding comparing elements.
A disadvantage of the above-described device is the complicated circuit embodying a complex operating algorithm as well as the use of an electric power supply circuit with two control inputs.